This invention relates to time assignment speech interpolation systems, and more particularly to a random access memory providing fixed and variable delays for such a system.
Because of the extremely high cost of communications transmission facilities, e.g. satellite channels and undersea transmission links, the prior art has sought various means to maximize the efficiency of existing transmission facilities. One such system is known as a time assignment speech interpolation (TASI) system. In a typical TASI system, calls from n callers are transmitted across, for example n/2 transmission facilities to a remote location. At that location, the n/2 facilities are connected to n output speech channels. TASI systems operate on the assumption, verified as a statistical fact, that at any given time not all callers will wish to talk simultaneously. In fact, as a general rule, callers are actively talking less than half of the time the talker and the listener are interconnected. Accordingly, TASI systems may be defined as switching systems which interconnect talker and listener only when the talker is actively speaking, provided there is a transmission facility available at that time.
"OVER-ALL CHARACTERISTICS OF A TASI SYSTEM" by J. M. Fraser, D. B. Bullock and N. G. Long, The Bell System Technical Journal, July 1962, pages 1439-1473 describes a TASI system. Such systems have been successfully used on undersea cables, for example, where a relatively large number of transmission facilities are available. Typically, thirty-six transmission facilities are available to transmit signals from seventy-four speech channels.
Another transmission facility, referred to as the order wire or control channel, is used to transmit disconnect signals to the remote location. FIG. 3 of the aforementioned article shows such a system.